An aortic dissection is a form of aneurysm which often occurs in the descending aorta, in which the wall of the vessel tears to such an extent that blood under pressure passes between inner and outer layers of the torn wall to expand part of the wall into an inflated sac or path of blood, referred to as a false lumen. The false lumen so formed may extend some distance along the descending thoracic and abdominal aorta and open out into the aorta again further down from the tear.
It has been found that dissections may self-heal if the proximal entry tear is covered to prohibit blood flow and pressure connection between the true and the false lumen at the proximal part of the dissected aorta. Consecutively the inner, separated, layer of vessel wall is pressed against the outer layer and the vessel wall may remodel over time. This can usually be achieved by the use of a stent graft positioned in the true lumen covering the proximal entrance to the false lumen and by means of a stent graft disposed along the length of the inner layer. The stent acts to cover intimal tears, which are connections between the true and the false lumen. They also press the inner wall layer against the outer wall layer and secure patency of the true lumen. It has been found, however, the vessel wall can remodel, that is become unitary again more likely if the wall layers are pressed together shortly after having separated. Once the dissection has become chronic, that is, it has existed for any length of time, it becomes less likely to achieve remodelling of the vessel wall. In such a circumstance, the wall layers remain separate and the false lumen persists. Dissections may remain undetected in a patient for significant periods, in which case they may be treated before becoming chronic.
While there is a false lumen in the vessel there is the risk of blood backflow through the downstream opening into the false lumen. This backflow maintains pressure in the false lumen and in particular between the inner and outer vessel wall layers. Such backflow contributes to a failure to close off the false lumen, aneurysmal widening of the false lumen and eventual risk of rupture of the outer vessel wall.
An example of a known dissection device and method is disclosed, for instance, in WO-2011/0270377.